Some RFID systems use reflected or “backscattered” radio frequency (RF) waves to transmit information from an RFID tag to an RFID reader. Passive tags harvest all of their operating power from the signal received from the reader; therefore passive tags are only powered when in the signal beam of the reader. When powered, the passive tags may receive and process the information received from the reader signal, whereupon the tag may communicate back to the reader using backscattering. However, as the distance between the tag and the reader increases, the power and signal strength decreases.
Thus passive RFID tags are limited to a certain distance from the RFID reader (e.g., a range) in which the power and signal strength are high enough to operate the passive tag. In conventional products, the ratio of the operating range with respect to the size of a tag has been significantly limited. For examples of such conventional disadvantages, see any of the following U.S. Pat. No. 4,123,754 entitled “Electronic detection and identification system”. U.S. Pat. No. 4,736,207 entitled “Tag device and method for electronic article surveillance”, U.S. Pat. No. 4,782,345 entitled “Transponder antenna”, U.S. Pat. No. 5,376,943 entitled “Moving vehicle transponder”, and U.S. Pat. No. 5,682,143 entitled “Radio frequency identification tag.”
The operating range of an RFID tag may be increased as the size of the tag itself is increased, however, this is unfavorable as it increases costs, as well as space required to house the enlarged tag itself. Further description of such unfavorable results can be found in U.S. Pat. No. 6,049,278 entitled “Monitor tag with patch antenna.”
Furthermore, semi-passive tags use a supplemental power source, e.g., battery, for tag operations when the tag is unable to harvest enough energy from the RF signal. While reader-to-tag communication distances are greatly increased relative to passive tags, the range of semi-passive tags is likewise limited. For further examples of such conventional disadvantages, see either of the following U.S. Pat. No. 5,392,049 entitled “Device for positioning a first object relative to a second object”, and U.S. Pat. No. 5,414,427 entitled “Device for information transmission.”